Chocolate Frosting (Sour Cream)

This is a rich dark chocolate frosting with a touch of tang thanks to sour cream. 

14 oz semisweet or bittersweet chocolate, chopped
¼ cup light corn syrup
2 cups sour cream
1½ tsp. kosher salt
1½ tsp. pure vanilla extract
2¾ cups powdered sugar
¾ cup (1½ sticks) unsalted butter, room temperature

Stir chocolate and corn syrup in a large metal bowl set over a large saucepan of simmering water until melted and smooth; remove from heat. Stir sour cream, salt, and vanilla in a medium metal bowl; set over same saucepan of simmering water. Stir until mixture is warm but not hot, about 2 minutes. Add sour cream mixture to chocolate mixture; stir until smooth and glossy. Set aside.

Using an electric mixer, beat powdered sugar and butter in a medium bowl until light and fluffy, 2-3 minutes. Scrape down sides of bowl. Slowly beat in chocolate mixture. Continue beating until no lumps remain, about 2 minutes.

Frosting should be smooth and shiny. Cover and chill until slightly firmed up, about 30 minutes.

Place 1 cake layer on a cake stand or large plate. Spoon ⅔ cup frosting over; using an offset spatula or the back of a spoon, smooth frosting to edge of cake, creating an even layer. Place another cake layer on top. Repeat with frosting and remaining cake layers. Spread remaining frosting over top and sides of cake.

Makes enough for a multi-layored cake.